A Method for Weak Lensing Flexion Analysis by the HOLICs Moment Approach

TL;DR

This paper introduces a new method for measuring weak gravitational flexion using the HOLICs moment approach, enabling accurate mass mapping of galaxy clusters even with complex PSF effects.

Contribution

The authors extend the HOLICs formalism to include higher-order lensing distortions and PSF effects, improving flexion measurement accuracy from observational data.

Findings

Successfully measured flexion in simulated and real data

Produced a high-resolution mass map of galaxy cluster A1689

Revealed bimodal mass distribution in the cluster core

Abstract

We have developed a method for measuring higher-order weak lensing distortions of faint background galaxies, namely the weak gravitational flexion, by fully extending the Kaiser, Squires & Broadhurst method to include higher-order lensing image characteristics (HOLICs) introduced by Okura, Umetsu, & Futamase. We take into account explicitly the weight function in calculations of noisy shape moments and the effect of higher-order PSF anisotropy, as well as isotropic PSF smearing. Our HOLICs formalism allows accurate measurements of flexion from practical observational data in the presence of non-circular, anisotropic PSF. We test our method using mock observations of simulated galaxy images and actual, ground-based Subaru observations of the massive galaxy cluster A1689 ($z=0.183$). From the high-precision measurements of spin-1 first flexion, we obtain a high-resolution mass map in the central region of A1689. The reconstructed mass map shows a bimodal feature in the central $4'\times 4'$ region of the cluster. The major, pronounced peak is associated with the brightest cluster galaxy and central cluster members, while the secondary mass peak is associated with a local concentration of bright galaxies. The refined, high-resolution mass map of A1689 demonstrates the power of the generalized weak lensing analysis techniques for quantitative and accurate measurements of the weak gravitational lensing signal.